1. Field of the Invention
The present invention relates to an electron beam exposure apparatus and an electron beam generating device for exposing a wafer by an electron beam. More particularly, it relates to an electron beam exposure apparatus and an electron beam generating device which prevents electric discharge between an insulator, on which an electron gun is mounted, and ground potential.
2. Description of Related Art
With miniaturization of semiconductor devices in recent years, improvement in irradiation uniformity of an electron beam in an electron beam exposure apparatus is required. The irradiation uniformity of the electron beam is deteriorated by change of potential difference between a cathode and a grid in the electron beam exposure apparatus, exhaustion of the cathode, etc. Conventionally, the potential difference between the cathode and the grid is adjusted by an element called self-bias resistance.
On the other hand, since there is no effective remedy for preventing the exhaustion of the cathode, it has been desired to extend the service life of the cathode. The cause of the cathode exhaustion greatly originates in decreasing of the degree of vacuum in the vacuum area of the electron beam exposure apparatus due to, for example, the electric discharge in the vicinity of the electron beam generating device. Discharge gas is generated in an electric discharge path by the energy release during the electric discharge, the discharge gas is ionized by the electron beam, and the cathode is spattered with the ionized discharge gas, by which the cathode is exhausted.
In the conventional electron beam exposure apparatus, thermal electrons emitted from cathode are accumulated in an insulating part of an insulator, the electric discharge occurs by the accumulated thermal electrons, and the degree of vacuum of the vacuum area is decreased. The electric discharge on the surface of the insulator generates the great amount of the discharge gas, and degrades the degree of vacuum more than an order of magnitude. Moreover, due to the electric discharge on the surface of the insulator, the acceleration voltage for accelerating the thermal electrons emitted from the cathode in the direction of the wafer is fluctuated, the current of the electron beam is also fluctuated, and accuracy of the wafer exposure was degraded.